1. Field of the Invention
The present invention relates to a device and a method for performing image processing to a moving image.
2. Description of the Related Art
A moving image captured by a digital video camera, a digital camera with a moving image shooting function, or the like is video signals containing 15 to 60 fields per second. The number of pixels per field in total of three colors (red (R), green (G), and blue (B)) is about 2 to 10 mega pixels. In order to enhance the image quality of the moving image, various processings are performed such as white balance adjustment, color correction for tuning to a desirable color, gamma correction (tone correction) for matching characteristics of the moving image with nonlinear output characteristics of output equipment (e.g., a cathode-ray tube or a monitor), edge enhancement for improving apparent resolution, a noise reduction processing.
Desirable output images for viewers are not always of faithfully reproduced colors of original colors in terms of photometry and colormetry. As for colors, it is known that there are colors called memory colors, which people prefer (typical colors of familiar objects which people tend to think of), such as a color of pure blue sky and a color of healthy skin. Parameters for image representation include a color as described above, a tone (gamma), an edge, and so on. People's preference for colors differs depending on subjects. For example, in case of taking a picture of landscape, more lively colors, harder gamma characteristics, and a sharper edge are likely to be preferred. In case of taking a picture of a person, a favorable skin color, softer gamma characteristics, and a softer edge are likely to be preferred. The landscape and people are often photographed together in one scene.
The skin color is an important color especially in terms of image representation. Japanese Patent No. 3387071 (hereinafter, referred to as Patent Document 1), for example, describes video equipment such as a television set or a camera, which tunes the skin color to a predetermined color known as a memory color. More specifically, Patent Document 1 discloses a technique of calculating a level of importance of every region formed of skin-color pixels (skin-color region) and a level of importance of a skin-color image. The level of importance of the skin-color region is defined in such a manner that, the larger the number of skin-color pixels or the closer the position of the region to the center of an image, the higher the value of the skin-color region. The level of importance of the skin-color image is calculated according to the level of importance of the skin-color region. Thus, the level of importance of the skin-color image is defined such that the larger the region of high importance contained in the image, the higher the level of importance. The level of importance of the image containing no skin-color region is set to zero. Many people prefer higher chroma for three primary colors in natural landscape such as blue of sky and green of plants, while preferring relatively lower chroma for a color of human skin, as compared with the above three primary colors in the natural landscape. Thus, it is possible to provide images giving good impression by setting the chroma such that the higher level of importance of the skin-color image the image has, the less the chroma of the skin color while the chroma of colors other than the skin color is constantly multiplied by a fixed number.
However, the technique disclosed in Patent Document 1 cannot provide most appropriately processed images in terms of viewers' point of view, because the chroma of the colors other than the skin color is always multiplied by a fixed number.
Moreover, the technique disclosed in Patent Document 1 cannot perform processing that distinguishes a moving object region and a still object region from each other.